Opening OST Files

The OST file type is primarily associated with Outlook.

OST	File extension: OST
	File type:	offline cache

What is an OST file?

OST files mostly belong to Outlook by Microsoft. An OST file contains a locally saved copy of emails, contacts, tasks, and calendar information synchronized or downloaded for an IMAP, Outlook, or Exchange email account. By saving a local copy of an email account's data as an OST file, Outlook is able to retrieve such information without Internet access. Messages, contacts, appointments and other entries created by a user when Outlook is offline are also saved in an OST file until Outlook is able to establish a connection to the email database. Another type of OST file is a construction and project takeoff estimate created by On-Screen Takeoff.

How to open OST files

You need a suitable software like Outlook to open an OST file. Without proper software you will receive a Windows message "How do you want to open this file?" or "Windows cannot open this file" or a similar Mac/iPhone/Android alert. If you cannot open your OST file correctly, try to right-click or long-press the file. Then click "Open with" and choose an application. You can also display a OST file directly in the browser:. Just drag the file onto this browser window and drop it.

Online OST Text Viewer

Choose your .ost file to analyze

or drag and drop it here

Online File Viewer

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Programs that open and convert OST files:

Outlook by Microsoft
See the previous paragraphs to learn more about the main application. OST files are often referred to as Outlook miscs because this type of file is primarily created or used by this software.
Exchange Server (offline cache) by Microsoft
Exchange Server is an email and calendar server application for Windows operating system. Its offline cache is saved in an OST file. This file format is classified as Misc. Related links: Introduction to Outlook Data Files (.pst and .ost), Open or import items from an offline Outlook Data File (.ost)
On-Screen Takeoff (project) by On Center Software
On-Screen Takeoff is a software for estimating construction takeoff costs and requirements. It saves a project in an OST file. This file format is classified as Data.
Tivoli Storage Manager (data) by IBM
Tivoli Storage Manager is a file backup application compatible with desktop and server operating systems. It saves some data in an OST file. This file format is classified as Data.

OST file format:

To view or edit OST files you need to know the file format, because it determines how the data in this file is stored. The file format can be determined based on the file extension and the signature (the first few characters of a file). However, different programs can use the same file extension. Furthermore, a file extension can be renamed incorrectly and double-clicking on it will then display an error when it is opened. So you need a detailed analysis of a file to find out the format and the associated program. Below you will find our evaluation of the OST files:

The OST file extension is rarely used and mainly uses a special format. The two most popular formats are as follows:

90% of all OST files are Outlook Exchange Offline Storage files. The contents of these files cannot be read by a human; only a computer program can interpret the data. Most of these files are 16 MB to 3 GB in size. It is a modern file type. Certain words are almost always found in the files, such as !BDN. These files can be linked to outlook, gmail and huser, and usually contain person-related data.

All the rest of the OST files (10%) have different formats. Often described as mangaccat or yahoo. Drag & drop your file here to see the file format and a preview of your OST file!

Technical Data for OST File Extension

File classification:

Misc

Related files:

nst, pst, oct, osd, prf, oab

Mime type:

application/vnd.ms-outlook-pst, application/vnd.ms-outlook

The following listing is compiled from the database produced by the 'Associate This!' program, selected data from the main FILExt database and file extension information submitted by users.

ProgramID: OSTFile, FileType: Office Data File

ProgramID: webfile, AppName: Dreamweaver MX

ProgramID: WEBFile, FileType: Office Data File

an ost offline cache is a special file format by Microsoft and should only be edited and saved with the appropriate software.

How to solve problems with OST files

Associate the OST file extension with the correct application.
Update your software that should actually open offline caches. Because only the current version supports the latest OST file format. Search, therefore, e.g. on the Microsoft manufacturer website after an available Outlook update.
To make sure that your OST file is not corrupted or virus-infected, get the file again and scan it with Google's virustotal.com.
Click here to open your .OST file online - secure, fast, and no downloads needed.